This invention relates to electronic identification of a pneumatic tire both during its manufacture and thereafter. More particularly, the invention relates to the combination of a pneumatic tire and an integrated circuit transponder located within the structure of the tire. The integrated circuit transponder is a passive device in that it has no source of electrical energy but instead depends upon the receipt of an "interrogation" signal emanating from a source outside of the tire. The interrogation signal is rectified by the integrated circuit transponder, which then utilizes the rectified signal as a source of electrical energy for use in its transmission of an electrical signal digitally encoded to identify the tire. A unique code can be used for each tire.
An "Identification System" is described in U.S. Pat. No. 4,730,188 issued Mar. 8, 1988, to Thomas A. Milheiser and assigned to Identification Devices, Inc. of Boulder, Colo. now known as Destron/IDI, Inc. of Boulder, Colo. The Milheiser patent describes a system which utilizes circuitry similar in many ways to prior-art circuitry described herein, the description herein being of an integrated circuit marketed by Destron/IDI. However, the circuitry described in the Milheiser patent is regarded by the inventors as being less desirable than the integrated circuit described herein and now sold by Destron/IDI.
The Milheiser patent describes a device called an "exciter" that is used to transmit the interrogation signal to the circuitry in the transponder used to identify an animal or article with which the transponder is associated for identification. The exciter consists of an A/C or oscillating radio frequency (R/F) signal source and power driver which provides a high current, high voltage excitation signal to an interrogator coil. The magnetic field propagated by the interrogator coil couples inductively to a very small coil associated with the circuitry of the transponder, thereby, inductively supplying A/C energy to the transponder circuitry.
One of the present inventors conceived the use of the inductively coupled R/F transponders manufactured by Identification Devices, Inc. in pneumatic tires prior to May, 1986, when such transponders were first built into passenger tires at facilities of Goodyear, the assignee of this invention, for evaluation. While such inductively-coupled transponders worked reasonably well in the passenger tire application, the development and product costs lead to reduced interest in the passenger tire application.
Interest in the use of the inductively-coupled transponder for radial-ply, all steel truck tires has continued, and Destron/IDI has installed inductively coupled transponders to the radially inner side of the innerliner in such pneumatic truck tires. The devices typically have been utilized with flat inductive coils, connected to an integrated circuit in the transponder. The flat coils and integrated circuit were embedded in a plastic material about the size and shape of a credit card. The "credit card" device then was inserted within the inside of an already cured pneumatic tire by adhering the device to the innerliner of the tire with a patch material. This identification technique requires special materials surrounding the "credit card" device, can only be used after tire vulcanization, and is expensive to implement. Moreover, the inductively-coupled exciter device used to interrogate the "credit card" integrated circuit transponder had to be located closer to the tire than is desirable.
It has been known by Destron/IDI and the present inventors that electric field or capacitive coupling of an A/C electric field into a transponder device is possible. This requires very strong electric fields in order to excite the transponder when the transponder is located in free space.
The inventors have discovered that a transponder which has separate first and second electrodes, rather than an inductive coil, for receipt of energy supplied by the oscillating electric field from the exciter can be used for a transponder positioned within a tire provided the transponder has its electrodes suitably designed and positioned within the tire structure with respect to its steel components. This capacitive coupling to the transponder can even be accomplished in a steel-reinforced radial ply truck tire in which the steel carcass ply forms an equipotential surface. Accordingly, the inventors have provided a combination tire and integrated circuit transponder which can withstand the severe environmental conditions a tire must endure during its manufacture and use and which can be used in automation of manufacturing, tracking of tires during and after manufacture, sorting, inventory control, shipping of the tire, statistical process control, field engineering, anti-theft, and control of truck tire retreading, and vehicle or trailer tire application or identification.